~~~
Before you read this, have a look at the DIFFERENCES and
-GVARIANT_SERIALIZATION texts, you find in the same directory where you
+GVARIANT_SERIALIZATION texts you find in the same directory where you
found this.
We invite you to port your favorite D-Bus protocol implementation
over to kdbus. However, there are a couple of complexities
involved. On kdbus we only speak GVariant marshaling, kdbus clients
ignore traffic in dbus1 marshaling. Thus, you need to add a second,
-GVariant compatible marshaler to your libary first.
+GVariant compatible marshaler to your library first.
After you have done that: here's the basic principle how kdbus works:
You connect to a bus by opening its bus node in /dev/kdbus/. All
-buses have a device node there, that starts with a numeric UID of the
+buses have a device node there, it starts with a numeric UID of the
owner of the bus, followed by a dash and a string identifying the
bus. The system bus is thus called /dev/kdbus/0-system, and for user
buses the device node is /dev/kdbus/1000-user (if 1000 is your user
CONNECTING
-To connect to a bus, simply open() its device node, and issue the
+To connect to a bus, simply open() its device node and issue the
KDBUS_CMD_HELLO call. That's it. Now you are connected. Do not send
Hello messages or so (as you would on dbus1), that does not exist for
kdbus.
The structure you pass to the ioctl will contain a couple of
-parameters that you need to know to operate on the bus.
+parameters that you need to know, to operate on the bus.
There are two flags fields, one indicating features of the kdbus
kernel side ("conn_flags"), the other one ("bus_flags") indicating
"incompatible" feature must not proceed with the connection.
The hello structure also contains another flags field "attach_flags"
-which indicates meta data that is optionally attached to all incoming
+which indicates metadata that is optionally attached to all incoming
messages. You probably want to set KDBUS_ATTACH_NAMES unconditionally
in it. This has the effect that all well-known names of a sender are
attached to all incoming messages. You need this information to
The kernel will also return the bloom filter size used for the signal
broadcast bloom filter (see below).
-The kernel will also return the bus ID of the bus in an 128bit field.
-
-The pool size field specifies the size of the memory mapped buffer,
-where received messages are placed by the kernel.
+The kernel will also return the bus ID of the bus in a 128bit field.
+The pool size field specifies the size of the memory mapped buffer.
After the calling the hello ioctl, you should memory map the kdbus
-fd. Use the pool size returned by the hello ioctl as map size. In this
-memory mapped region the kernel will place all your incoming messages.
+fd. In this memory mapped region, the kernel will place all your incoming
+messages.
SENDING MESSAGES
items. The former contain an offset and size into your memory mapped
pool where you find the payload.
-If during the HELLO ioctl you asked for getting meta data attached to
+If during the HELLO ioctl you asked for getting metadata attached to
your message, you will find additional KDBUS_ITEM_CREDS,
KDBUS_ITEM_PID_COMM, KDBUS_ITEM_TID_COMM, KDBUS_ITEM_TIMESTAMP,
KDBUS_ITEM_EXE, KDBUS_ITEM_CMDLINE, KDBUS_ITEM_CGROUP,
(bits in the filter), k=8 (nr of hash functions). The underlying hash
function is SipHash-2-4. We calculate two hash values for an input
strings, one with the hash key b9660bf0467047c18875c49c54b9bd15 (this
-is supposed to be read as a series of 16 hexadecimially formatted
+is supposed to be read as a series of 16 hexadecimal formatted
bytes), and one with the hash key
aaa154a2e0714b39bfe1dd2e9fc54a3b. This results in two 64bit hash
values, A and B. The 8 hash functions for the bloom filter require a 9
KDBUS_CMD_MEMFD_SIZE_SET. Note that memfds will be increased in size
automatically if you touch previously unallocated pages. However, the
size will only be increased in multiples of the page size in that
-case. Thus, in almost all cases, an explicitl KDBUS_CMD_MEMFD_SIZE_SET
+case. Thus, in almost all cases, an explicit KDBUS_CMD_MEMFD_SIZE_SET
is necessary, since it allows setting memfd sizes in finer
granularity. To seal a memfd use the KDBUS_CMD_MEMFD_SEAL_SET ioctl
call. It will only succeed if the caller has the only fd reference to
A couple of messages previously generated by the dbus1 bus driver are
now generated by the kernel. Since the kernel does not understand the
payload marshaling, they are generated by the kernel in a different
-format. This is indicated with a the "payload type" field of the
+format. This is indicated with the "payload type" field of the
messages set to 0. Library implementations should take these messages
and synthesize traditional driver messages for them on reception.
When a method call fails because the peer terminated the connection
before responding, a KDBUS_ITEM_REPLY_DEAD message is
- generated. Simiarly, it should be synthesized into a method error
+ generated. Similarly, it should be synthesized into a method error
reply message.
For synthesized messages we recommend setting the cookie field to
broadcasting in the kernel. The receiver should not rely on this data
to be around though, even though it will be correct if it happens to
be attached. In order to avoid programming errors in applications, we
-recommend though not to pass this data on to clients that did not
+recommend though not passing this data on to clients that did not
explicitly ask for it.
Credentials may also be queried for a well-known or unique name. Use
This will ensure that kdbus is preferred over the legacy AF_UNIX
socket, but compatibility is kept. For the user bus use:
- kernel:path=/dev/kdbus/$UID-system/bus;unix:path=$XDG_RUNTIME_DIR/bus
+ kernel:path=/dev/kdbus/$UID-user/bus;unix:path=$XDG_RUNTIME_DIR/bus
With $UID replaced by the callers numer user ID, and $XDG_RUNTIME_DIR
following the XDG basedir spec.
~ianmdlvl / elogind.git / blobdiff